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packed. The tube is attached to a thermometer (preferably with
a very small bulb) so that the substance is level with the bulb. The
attachment may be made by a narrow rubber rintf or by simply
moistening the side* of the capillary with the thermometer bulb,
which has been dipped in the liquid in the bath, and then
pressing it against the thermometer stem. The thermometer
passes through a cork inserted into a round flask with a Ionj»'
neck, the bull* of which is throe-quarters filled with concentrated
sulphuric: acid, }*lyi:erol, ur castor oil. The ik»bk is clumped to a

retort stand and is heated very gradually by a small flame. In-
stead oi «lamping the flask to a rclort stand* it <"an be fixed in a
small brass tripod, shown in Kig. 53, which fits on to an ordinary
laboratory tripod and from which it can be removed when not
required,1 When a certain temperature is reached the substance,
if pure, melts suddenly within-one or two degrees. When
approaching the melting-point, it is desirable to remove the
flame or turn if very low so that the rise of temperature is very
gradual If the liquefaction is protracted, it is an indication
that the substance is not pure. The melting-point, obtained in
this way, lu be quite accurate, must be corrected for the

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